Electrochemical oxidation of lignin at IrO2-based oxide electrodes

In this study, four IrO2-based electrodes (Ti/Ta2O5–IrO2, Ti/SnO2–IrO2, Ti/RuO2–IrO2 and Ti/TiO2–IrO2) were fabricated using the thermal decomposition method. Their morphology and composition were characterized using scanning electron microscope (SEM) and X-ray energy dispersive spectrometry (EDS). The stability and electrocatalytic activity of the prepared IrO2-based electrodes were investigated. The catalytic activity of the prepared electrodes was examined for the electrochemical oxidation of lignin. In situ UV/vis spectroscopy was used to monitor the concentration changes of lignin with time and to study the kinetics of the electrochemical oxidation of lignin. The effects of the temperature and the applied current densities on the oxidation of lignin were also investigated. HPLC was employed to identify the products resulting from the electrochemical oxidation of lignin, revealing that the primary products were vanillin and vanillic acid. Our study shows that in situ UV–vis spectroscopy is an effective technique to study the kinetics of electrochemical oxidation of lignin and that the Ti/RuO2–IrO2 electrode exhibits the highest stability and activity for lignin degradation among the four IrO2-based electrodes which makes it a promising electrode for the electrochemical oxidation of lignin to value-added products.